Magnetic materials



Patented May 18 1948 Ethan AQNesbitt, Chatham, N. .L, assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 10, 1945,

Serial No. 604,295

No Drawing.

' 2 Claims. 1

permanent magnets by a cold working treatment. a

The invention also relates to and includes methods of treating and producing such improved alloys and permanent magnets.

An object of the invention is the production of better and more efficient permanent magnet materials.

This present application is a continuation-inpart of my copending application, Serial ,No. 416,216, filed October 23, 1941, which is now Patent No. 2,382,649 dated August 14, .1945, and which in turn was a continuation-in-part of a former application copending therewith, namely, Serial No. 311,735, filed December 30, 1939, which is now Patent No. 2,298,225, dated October 6, 1942; for which reason the priority benefits of the filing dates of said applications are claimed for the present application to whatever extent and under whatever conditionsof law maybe applicable. I

A feature of the present invention is the discovery that permanent magnet compositions, such as those described hereinafter, may be improved by reduction of the cross section thereof by a stage of cold working during their preparation and prior to the final heat treatment. Such Working is preferably accomplished by methods which produce elongation and prevent lateral spreading. Methods that have been found beneficial include swaging, rollin'g with grooved rolls and wire drawing. It appears that the result of improved permanent magnet properties is manifested chiefly in the direction of elongation. Reduction of thickness by such rolling of a metal sheet as permits the material to spread laterally is only partially effective.

The evidence is that materials of or produced according to the present invention generally are anisotropic and their improved properties are manifested chiefly in the direction in which the elongation takes place.

In the said application, Serial No.31l,735, it is pointed out that there are classes of materials which, if maintained at a certain temperature but below the melting point, assume a form known as the "gamma phase, and if the material is thereafter cooled 'to around room temperature it tends to assume the alpha phase and thereafter if maintained at around 500 to 800, a finely dispersed small amount of the gamma phase forms in the alpha phase.

This brief statement is to be read in the light of the information, diagrams, and discussion application, Serial No. 311,735.

As pointed out in the said application, now Patent No. 2,298,225 dated October 6, 1942, a suitable, procedure for preparing permanent magnet material is to melt the material and cool it .to room temperature to produce formation of the alpha phase and thereafter elevate the material to a higher temperature between 500 C. to 800 C. for a length of time such as is necessary to allow a small amount of the "gamma phase to precipitate in a highly dispersed form in the alpha phase. This produces dispersion hardening in the material and produces a very effective permanent magnet material. This method of forming permanent'magnet materials is dlfi'erent andseemingly involves a different principle from that heretofore employed with respect to many others, such as alloys of iron, cobalt and molybdenumin that, in the present instance, the material is converted into a low temperature alpha phase and thereafter has a small amount of the high temperature gamma. phase precipitated therein in a fine and dispersed state. In the usual case. of permanent magnets hardened by precipitation the high temperature phase is preserved and a small amount of the low temperature phase is precipitated.

In some alloys of the type under discussion'the gamma to alpha tranformation tends to occur at low temperatures atwhich the transformation becomes sluggish and non-equilibrium conditions exist.

Whether this is the case or not, cold rolling these alloys in grooved rolls or working them mechanically b any equivalent method causes or expedites the formation at room temperature of the alpha phase and brings them into equilibrium. Some alloys of this type may not change completely tothe alpha phase at room temperature unless given the above treatment. Others change to alpha phase only in part. This result whether whole or partial is one beneficial aspect of the present invention. However, there is a second beneficial aspect which is due to crystal orientation. X-ray measurements confirm this and magnetic tests show the best permanent magnet properties in the direction of elongation. Either or both of these beneficial aspects maybe present in varying degrees.

After the alloys are brought completely or mainly into the alpha phase by the combinationof cooling and cold working theyare raised of said to a temperature in the range of temperatures 55.

which causes theprecipitation in finely dispersed particles of some of the gamma phase. This results in the production of magnetic material having effective and desirable properties as permanent magnets in the direction of elongation. In every case care must be used not to raise the material to too high a temperature in order not to lose the effect of cold working.

A frequently used criterion of the desirability of permanent magnet materials is the product of coercive force and residual induction. A more accurate figure of merit is that of maxi mum energy product, which on the demagnetization portion of the hysteresis loop, is the prodnot is induction B and magnetizing force Hat a point where this product is the greatest. See Wahl, Applied Magnetism, pages 42 to 45 inelusive.

The above criterion is independent of the matter of cost, ease or difliculty of preparation, roll ing or drawing, brittleness, availability of raw materials and other factors which must receive consideration for many practical purposes and applications. Thus a permanent magnet composition which has an absolute maximum energy product less than some other which is less available or suitable from some one or more of the above aspects may be a valuable contribution to the art if, for example, it may be made to possess a. considerably greater maximum energy product.

. Among objects of the present invention are to provide better permanent magnets at little or no increase in cost; to produce useful permanent magnets from materials not hitherto known to possess permanent magnet properties to a useful extent; to improve the properties of compositions known to have useful permanent magnet properties; to produce useful permanent magnets from cheap or readily available raw materials; to increase either or both the product of coercive force and residual induction or the "maximent at around 800 to 1300 C. The cooled material, which may be cooled to room temperature slowly or rapidly, and must be cooled substantially below about 600 C. is forcibly elongated by rolllng with grooved rolls, swaging, drawing through dies or by combinations of these methods or by any similar method or methods so as to reduce the cross section in one or several steps over a range from a small amount to a small fraction of the original cross section. The

material is then heated to a temperature generally in the region 500 to 800 C. and maintained; for a sufiicient time such as a matter of seconds or minutes at the higher temperature to one to'several hours at the lower temperature,

mum energy product of magnetic materials; to

provide elongated magnetic materials such as tapes and strips having useful maximum energy products; and to provide useful magnets from materials which may be worked with facility.

The subject-matter of the invention or discovery comprises a range or group of magnetic alloys which by appropriate combined heat treat- -ment and cold rolling or elongating treatment will have one or the other or both of the abovenamed magnetic products or the coercive force or the residual induction increased in the direction of elongation by from one hundred to several hundred per cent as compared to the material in the cast or unsuitably heat treated or unsuitably worked condition. 0

A feature of the invention or discovery is the lack of any necessity for quenching the material at any time in order to improve its properties; however, rapid cooling after casting may be practiced. One of the beneficial aspects of the discovery is that the cooling rates may vary widely as convenience or necessity demands.

The alloys may be prepared in the form of rods, bars, wire or tapes. A suitable treatment for any specimen is first to give it the desired amount of cold working plus a low temperature bake. No other heat treatment is necessary.

Satisfactory results have been obtained with reductions in area of 75 per cent, although this exact amount is by no means critical.

In greater detail, the material is cast, which gives it the necessary high temperature treatment; it may be given a further or special heat treatuproaches the bottom of the range.

Too high a temperature destroys the effect of the cold rolling;.and too low a temperature or too short a time is only partially eifective. A quenching treatment is unnecessary.

A composition which responds to this type of treatment is:

Per cent Per cent 5223 31 Per cent Iron Cobalt nesge Vanadium Carbon above about 0.1 per cent is not an essential constituent and in fact is absent from these materials. 7

The constituents may in general vary over a range'which includes iron from 78 per cent to 82 per cent, manganese from 14 per cent'to 18 per cent, and. vanadium from 3 per cent'to 5 per cent. Impurities incident to commercially available metals may amount to about 1 per cent maximum with the exception of carbon which, as stated above, is restricted in amount.

Thus there are described certain permanent magnet materials, an improvement in them by a heat treatment, a further and often, considerable improvement by a cold working treatment, and avoidance of necessity for quenching. These compositions possess or may be made to possess substantial permanent magnet properties and are notably improved in properties by a treatment of the kind described. They may be prepared from raw materials which are ordinarily cheap and readily available. They respond to the described treatment and may be made. to acquire magnetic properties increased as a result of the treatment described as. compared, with identical compositions as cast. In some cases the increase in energy product due to cold rolling may be per cent as comparedto the same material heat treated but not cold rolled. V

The apparatus illustrated in the above-noted Patent 2,298,225,0r any other suitable apparatus, may be used to perform the cold rollingor elonating process.

The finished magnets may be. magnetized by any of the usually employed methods or employed in any usual manner as recording tape or wire.

What is claimed is: I,

1. A composition adapted for permanent magnet use comprising 78 per cent to 82 per cent iron,

I 14 per cent to 18 per centmanganese, and 3 per of from 800 C. to 1300 emes 2'. An article having properties adapted for permanent magnet use composed of an alloy comprising as essential constituents 78 per cent to 82 per cent iron, 14 per cent to 18 per cent manganese, and 3 per cent to 5 per cent vanadium, these constituents comprising the entire constituents of the composition except for minor impurities not over 1 per cent, said article produced by passing the alloy into the temperature range 0., cooling it substantially below 600 0., forcibly elongating the material in the cold condition and thereafter maintaining it in the range 500 C. to 800 C. without exceeding about 800 C. whereby the material is caused to have increased ability to retain permanent magnetism in the direction of elongation.

ETHAN A. NESBITT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Nesbitt Aug. 14, 1945 Number 

